The aim of the proposed study is to extend our knowledge about the developmental course of aggression and delinquency among urban boys and girls from different ethnic backgrounds living in communities characterized by high rates of poverty, violence and crime. This study will build on the scientific value of an existing, developmental database employing an accelerated longitudinal design and involving eight successive cohorts of children. These children initially participated in the study when they were in the 2nd or 5th grade and they were randomly assigned to either an intervention or a no treatment control condition. This application seeks funding to analyze data on the 1017 children who received parental permission to participate and were assigned to the control condition. A particular focus of this research is to examine the evolving and reciprocal relations between social-cognitive variables, neighborhood violence, peer influences, and aggressive/delinquent behavior. In addition to examining trajectories and growth curves of aggression, delinquency and social cognition, these data will permit examination of the extent to which the course of aggression and delinquency is influenced specifically by contextual factors including neighborhood violence, peers' aggressive behavior, peers' social cognitions, and peer relations and how developing trajectories of aggression and delinquency influence some contextual factors (e.g., selections of antisocial peers) in a transactional process. The proposed set of studies can provide a bridge between psychological investigations of aggression and delinquency focused on social-cognitive and early peer relationship factors (e.g., peer rejection) and sociological studies of peer influences on adolescent delinquency focused on both the behavior and beliefs of the antisocial peer group. Because the data set includes both boys and girls from different ethnic groups, it will be possible to examine whether these individuals and contextual influences vary systematically by gender and ethnicity.